Inverter power supply and ballast circuit

ABSTRACT

A compact screw-in fluorescent lamp is mounted on an ordinary Edison-type screw-base. An inverter-type ballast is integrally included with the base, thereby making the fluorescent lamp capable of being screwed into an ordinary lamp socket and to be powered therefrom by ordinary power line voltage. The fluorescent lamp is folded and has a narrowed section of glass. The inverter-type ballast is powered via a voltage doubler and powers the fluorescent lamp via an tuned L-C circuit. Light output can be adjusted by way of an adjustment means functional to adjust the inverter frequency, thereby correspondingly to adjust the magnitude of the lamp current.

BACKGROUND OF THE INVENTION Related Applications

The present application is a Continuation-in-Part of Ser. No. 06/787,692filed 10/15, 1985 now abandoned; which is a continuation of Ser. No.06/644,155 filed 08/27/84, now abandoned; which was a continuation ofSer. No. 06/555,426 filed 11/23/83, now abandoned; which was acontinuation of Ser. No. 06/178,107 filed 08/14/80, now abandoned.

FIELD OF INVENTION

This invention relates to gas discharge lighting means as well as powersupplies particularly useful for ballasting gas discharge lamps.

DESCRIPTION OF PRIOR ART

For a description of pertinent prior art, reference is made to U.S. Pat.No. 4,677,345 to Nilssen; which patent issued from a Division ofapplication Ser. No. 06/178,107 filed 08/14/80; which application is theoriginal progenitor of instant application.

Otherwise, reference is made to the following U.S. Pat. Nos. 3,263,122to Genuit; 3,320,510 to Locklair; 3,996,493 to Davenport et el.;4,100,476 to Ghiringhelli; 4,262,327 Nilssen; and 4,857,806 to Nilssen.

SUMMARY OF THE INVENTION Objects of the Invention

An object of the present invention is that of providing a controllablepower supply for gas discharge lamps.

Another object is that of providing a compact folded screw-influorescent lamp.

Yet another object is that of providing means for adjusting the lightoutput. of gas discharge lamps.

These as well as other objects, features and advantages of the presentinvention will become apparent from the following description andclaims.

BRIEF DESCRIPTION

The present invention is directed to providing improved gas dischargelighting means and inverter circuits for powering and controlling gasdischarge lamps. The inverter circuits according to the presentinvention are highly efficient, can be compactly constructed and areideally suited for energizing gas discharge lamps, particularly compactfolded "instant-start" "self-ballasted" fluorescent lamps.

According to one feature of the present invention, a series-connectedcombination of an inductor and a capacitor is provided in circuit withthe inverter transistors to be energized upon periodic transistorconduction. Transistor drive current is preferably provided through theuse of at least one saturable inductor to control the transistorinversion frequency to be equal to or greater than the nature resonantfrequency of the inductor and capacitor combination. The high voltagesefficiently developed by loading the inverter with the inductor andcapacitor are ideally suited for energizing external loads such as gasdischarge lamps. In such an application, the use of an adjustableinductor permits control of the inverter output as a means of adjustingthe level of lamp illumination.

According to another feature of the present invention, reliable andhighly efficient half-bridge inverters include a saturable inductor in acurrent feedback circuit to drive the transistors for alternateconduction. The inverters also include a load having an inductancesufficient to effect periodic energy storage for self-sustainedtransistor inversion. Importantly, improved reliability is achievedbecause of the relatively low and transient-free voltages across thetransistors in these half-bridge inverters.

Further, according to another feature of the present invention, noveland economical power supplies particularly useful with the disclosedinverter circuits convert conventional AC input voltages to DC forsupplying to the inverters.

Yet further, according to still another feature of the invention, arapid-start fluorescent lamp is powered by way of a series-resonant LCcircuit; while heating power for the lamp's cathodes is provided vialoosely-coupled auxiliary windings on the tank inductor of the LCcircuit. Alternatively, cathode heating power is provided fromtightly-coupled windings on the tank inductor; in which case outputcurrent-limiting is provided via a non-linear resistance means, such asan incandescent filament in a light bulb, connected in series with theoutput of each winding.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a front elevation of a folded fluorescent lamp unit adaptedfor screw-in insertion into a standard Edison incandescent socket;

FIG. 2 is a schematic diagram illustrating the essential features of apush-pull inverter circuit particularly suitable for energizing the lampunit of FIG. 1;

FIG. 3A-3D is a set of waveform diagrams of certain significant voltagesand currents occurring in the circuit of FIG. 2;

FIG. 4 is a schematic diagram of a DC power supply connectable to both120 and 240 volt AC inputs;

FIG. 5 is a schematic diagram which illustrates the connection of anon-self-ballasted gas discharge lamp unit to the FIG. 2 invertercircuit;

FIG. 6 is a schematic diagram which illustrates the use of a toroidheater for regulation of the inverter output;

FIG. 7 is an alternate form of push-pull inverter circuit accordind tothe present invention;

FIG. 8 is a schematic diagram showing the connection of a gas dischargelamp of the "rapid-start" type to an inductor-capacitor-loaded inverteraccording to the present invention;

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 illustrates a screw-in gas discharge lamp unit 10 comprising afolded fluorescent lamp 11 suitably secured to an integral base 12. Thelamp comprises two cathodes 13, 14 which are supplied with the requisitehigh operating voltage from a frequency-converting power supply andballasting circuit 16; which, because of its compact size, convenientlyfits within the base 12.

The inverter circuit 16 is connected by leads 17, 18 to a screw-typeplug 19 adapted for screw-in insertion into a standard Edison-typeincandescent lamp socket at which ordinary 120 Volt/60 Hz power linevoltage is available. A ground plane comprising a wire or metallic strip21 is disposed adjacent a portion of the fluorescent lamp 11 as astarting aid. Finally, a manually rotatable external knob 22 isconnected to a shaft for mechanical adjustment of the air gap of aferrite core inductor to vary the inductance value thereof in order toeffect adjustment of the inverter voltage output connected to electrodes13, 14 for controlled variation of the lamp illumination intensity.

With reference to FIG. 2, a power supply 23, connected to a conventionalAC input, provides a DC output for supplying a high-efficiency invertercircuit 24. The inverter is operable to provide a high voltage to anexternal load 26, which may comprise a gas discharge device sich as thefluorescent lamp 11 of FIG. 1.

The power supply 23 comprises bridge rectifier having four diodes 27,28, 29 and 31 connectable to a 240 volt AC supply at terminals 32, 33.Capacitors 34, 36 are connected between a ground line 37 (in turndirectly connected to the inverter 24) and to a B+ line 38 and a B- line39, respectively. The power supply 23 also comprises a voltage doublerand rectifier optionally connectable to a 120 volt AC input takenbetween the ground line 37 and terminal 33 Or 32. The voltage doublerand rectifier means provides a direct electrical connection by way ofline 37 netween one of the 120 volt AC power input lines and theinverter 24, as shown in FIG. 2. The bridge rectifier and the voltagedoubler and rectifier provide substantially the same DC output voltageto the inverter 24 whether the AC input is 120 or 240 volts. Typicalvoltages are +160 volts on the B+ line 38 and -160 volts on the B- line39.

With additional reference to FIG. 4, which shows an alternate powersupply 23', the AC input, whether 120 or 240 volts, is provided atterminals 32' and 39. Terminal 39 is in turn connected through asingle-pole double-throw selector switch 41 to terminal 37' (for 120volt operation) or terminal 33' (for 240 volt operation). In all otherrespects, power supplies 23 and 23' are identical.

The inverter circuit 24 of FIG. 2 is a half-bridge inverter comprisingtransistors 42, 43 connected in series across the DC voltage output ofthe power supply 23 on B+ and B- lines 38 and 39, respectively. Thecollector of trasistor 42 is connected to the B+ line 38, the emitter oftransistor 42 and the collector of transistor 43 are connected to amidpoint line 44 (designated "M") and the emitter of transistor 43 isconnected to the B- line 39. The midpoint line 44 is in turn connectedto the ground line 37 through primary winding 46 of a toroidal saturablecore transformer 47, a primary winding 48 on an identical transformer49, an inductor 51 and a series-connected capacitor 52. The inductor 51and capacitor 52 are energized upon alternate transistor conduction in amanner to be described later.

An external load 26 is preferably taken off capacitor 52, as shown inFIG. 2. The inductor 51, preferably a known ferrite core inductor, hasan inductance variable by mechanical adjustment of the air gap in orderto effect variation in the level of the inductor and capacitor voltageand hence the power available to the load, as will be described. Whenthe load is a gas discharge lamp such as lamp 11 in FIG. 1, variation inthis inductance upon rotation of knob 22 accomplishes a lamp dimmingeffect.

Drive current to the base terminals of transistors 42 and 43 is providedby secondary windings 53, 54 of transformers 49, 47, respectively.Winding 53 is also connected to midpoint lead 44 through a biascapacitor 56, while winding 54 is connected to the B- lead 39 through anidentical bias capacitor 57. The base terminals of transistors 42 and 43are also connected to lines 38 and 44 through bias resistors 58 and 59,respectively. For a purpose to be described later, the base oftransistor 42 can be optionally connected to a diode 61 and a seriesZener diode 64 in turn connected to the midpoint line 44; similarly, adiode 63 and series Zener diode 64 in turn connected to the B- line 39can be connected to the base of transistor 43. Shunt diodes 66 and 67are connected across the collector-emitter terminals of transistors 42and 43, respectively. Finally, a capacitor 68 is connected across thecollector-emitter terminals of transistor 43 to restrain the rate ofvoltage rise across those terminals, as will be seen presently.

The operation of the circuit of FIG. 2 can best be understood withadditional reference to FIG. 3, which illustrates significant portionsof the waveforms of the voltage at midpoint M (FIG. 3A), thebase-emitter voltage on transistor 42 (FIG. 3B), the current throughtransistor 42 (FIG. 3C), and the capacitor 52 voltage and the inductor51 current (FIG. 3D).

Assuming that transistor 42 is first to be triggered into conduction,current flows from the B+line 38 through windings 46 and 38 and theinductor 51 to charge capacitor 52 and returns through capacitor 34(refer to the time period designated I in FIG. 3). When the saturableinductor 49 saturates at the end of period I, drive current to the baseof transistor 42 will terminate, causing voltage on the base of thetransistor to drop to the negative voltage stored on the bias capacitor56 in a manner to be described, causing this transistor to becomenon-conductive. As shown in FIG. 3c, current-flow in transistor 43terminates at the end of period I.

Because the current through inductor 51 cannot change instantaneously,current will flow from the B- bus 39 through capacitor 68, causing thevoltage at midpoint line 44 to drop to -160 volts (period II in FIG. 3).The capacitor 68 restrains the rate of voltage change across thecollector and emitter terminals of transistor 42. The current throughthe inductor 51 reaches its maximum value when the voltage at themidpoint line 44 is zero. During period III, the current will continueto flow through inductor 51 but will be supplied from the Bbus throughthe shunt diode 67. It will be appreciated that during the latter halfof period II and all of period III, positive current is being drawn froma negative voltage; which, in reality, means that energy is beingreturned to the power supply through a path of relatively low impedance.

When the inductor current reaches zero at the start of period IV, thecurrent through the primary winding 46 of the saturable inductor 47 willcause a current to flow out of its secondary winding 54 to causetransistor 43 to become conductive, thereby causing a reversal in thedirection of current through inductor 51 and capacitor 52. Whentransformer 47 saturates at the end of period IV, the drive current tothe base of transistor 43 terminates and the current through inductor 51will be supplied through capacitor 68; causing the voltage at midpointline 44 to rise (period V). When the voltage at the midpoint line Mreached 160 volts, the current will then flow through shunt diode 66(period VI). The cycle is then repeated.

As seen in FIG. 3, saturable transformers 47, 49 provide transistordrive current only after the current through inductor 51 has diminishedto zero. Further, the transistor drive current is terminated before thecurrent through inductor 51 has reached its maximum amplitude. Thiscoordination of base drive current and inductor current is achievedbecause of the series-connection between the inductor 51 and the primarywindings 46, 48 of saturable transformers 47, 49, respectively.

The series-connected combination of the inductor 51 and the capacitor 52is energized upon the alternate conduction of transistors 42 and 43.With a large value of capacitance of capacitor 52, very little voltagewill be developed across its terminals. As the value of this capacitanceis decreased, however, the voltage across this capacitor will increase.As the value of the capacitor 52 is reduced to achieve resonance withthe inductor 51, the voltage on the capacitor will rise and becomeinfinite in a loss-free circuit operating under ideal conditions.

It has been found desirable to regulate the transistor inversionfrequency, determined mainly by the saturation time of the saturableinductors 47, 49, equal to or higher than the natural resonancefrequency of the inductor and capacitor combination in order to providea high voltage output to external load 26. A high voltage acrosscapacitor 52 is efficiently developed as the transistor inversionfrequency approaches the natural resonant frequency of the inductor 51and capacitor 52 combination. Stated another way, the conduction periodof each transistor is desirably shorter in duration than one quarter ofthe full period corresponding to the natural resonant frequency of theinductor and capacitor combination. When the inverter 24 is used with aself-ballasted gas discharge lamp unit, it has been found that theinversion frequency can be at least equal to the natural resonantfrequency of the tank circuit. If the capacitance value of capacitor 52is reduced still further beyond the resonance point, unacceptably hightransistor currents will be experienced during transistor switching andtransistor burn-out will occur.

It will be appreciated that the sizing of capacitor 52 is determined bythe application of the inverter circuit 24. Variation in the values ofthe capacitor 52 and the inductor 51 will determine the voltagesdeveloped in the inductor-capacitor tank circuit. The external load 26may be connected in circuit with the inductor 51 (by a winding on theinductor, for example) and the capacitor may be omitted entirely. If thecombined circuit loading of the inductor 51 and the external load 26 hasan effective inductance of value sufficient to effect periodic energystorage for self-sustained transistor inversion, the current feedbackprovided by the saturable inductors 47,49 will effect alternatetransistor conduction without the need for additional voltage feedback.When the capacitor 52 is omitted, the power supply 23 provides a directelectrical connection between one of the AC power input lines and theinverter load circuit.

Because the voltages across transistors 42, 43 are relatively low (dueto the effect of capacitors 34, 36), the half-bridge inverter 24 is veryreliable. The absence of switching transients minimizes the possibilityof transistor burn-out.

The inverter circuit 24 comprises means for supplying reverse bias tothe conducting transistor upon saturation of its associated saturableinductor. For this purpose, the capacitors 56 and 57 are charged tonegative voltages as a result of reset current flowing into secondarywindings 53, 54 from the bases of transistors 42, 43, respectively. Thisreverse current rapidly turns off a conducting transistor to increaseits switching speed and to achieve inverter circuit efficiency in amanner described more fully in my co-pending U.S. patent applicationSer. No. 103,624 filed Dec. 14, 1979 and entitled "Bias Control for HighEfficiency Inverter Circuit" (now U.S. Pat. No. 4,307,353). The morenegative the voltage on the bias capacitors 56 and 57, the more rapidlycharges are swept out of the bases of their associated transistors upontransistor turn-off.

When a transistor base-emitter junction is reversely biased, it exhibitsthe characteristics of a Zener diode having a reverse breakdown voltageon the order of 8 to 14 Volt for transistors typically used inhigh-voltage inverters. As an alternative, to provide a negative voltagesmaller in magnitude on the base lead of typical transistor 42 duringreset operation, the optional diode 61 and Zener diode 62 combinationcan be used. For large values of the bias capacitor 56, the base voltagewill be substantially constant.

If the load 26 comprises a gas discharge lamp, the voltage across thecapacitor 52 will be reduced once the lamp is ignited to preventvoltages on the inductor 51 and the capacitor 52 from reachingdestructive levels. Such a lamp provides an initial time delay duringwhich a high voltage, suitable for instant starting, is available.

FIG. 5 the use of an alternate load 26' adapted for plug-in connectionto an inverter circuit such as shown in FIG. 2. The load 26' consists ofa gas discharge lamp 71 having electrodes 72, 73 and connected in serieswith a capacitor 74. The combination of lamp 71 and capacitor 74 isconnected in parallel with a capacitor 52' which serves the same purposeas capacitor 52 in the FIG. 2 circuit. However, when the load 26' isunplugged from the circuit, the inverter stops oscillating and thedevelopment of high voltages in the inverter is prevented. The fact thatno high voltages are generated by the circuit if the lamp isdisconnected while the circuit is oscillating is important for safetyreasons.

FIG. 6 illustrates a capacitor 52" connected in series with an inductor51" through a heater 81 suitable for heating the toroidal inductors 47,49 in accordance with the level of output. The load 26" is connectedacross the series combination of the capacitor 52" and the toroidheater. The heater 81 is preferably designed to controllably heat thetoroidal saturable inductors in order to decrease their saturation fluxlimit and hence their saturation time. The result is to decrease theperiodic transistor conduction time and thereby increase the transistorinversion frequency. When a frequency-dependent impedance means, thatis, an inductor or a capacitor, is connected in circuit with the ACvoltage output of the inverter, change in the transistor inversionfrequency will modify the impedance of the frequency-dependent impedancemeans and correspondingly modify the inverter output. Thus as the levelof the output increases, the toroid heater 81 is correspondinglyenergized to effect feedback regulation of the output. Further,transistors 42, 43 of the type used in high voltage inverters dissipateheat during periodic transistor conduction. As an alternative, thetoroid heater 81 can use this heat for feedback regulation of the outputor control of the temperature of transistors 42, 43.

The frequency dependent impedance means may also be used in a circuit toenergize a gas discharge lamp at adjustable illumination levels.Adjustment in the inversion frequency of transistors 42, 43 results incontrol of the magnitude of the AC current supplied to the lamp. This ispreferably accomplished where saturable inductors 47, 49 have adjustableflux densities for control of their saturation time.

FIG. 7 schematically illustrates an alternate form of inverter circuit,shown without the AC to DC power supply connections for simplification.In this Figure, the transistors are connected in parallel rather than inseries but the operation is essentially the same as previouslydescribed.

In particular, this circuit comprises a pair of alternately conductingtransistors 91, 92. The emitter terminals of the transistors areconnected to a B- line 93. A B+ lead 94 is connected to the center-tapof a transformer 96. In order to provide drive current to thetransistors 91, 92 for control of their conduction frequency, saturableinductors 97, 98 have secondary windings 99, 101, respectively, eachsecondary winding having one end connected to the base of its associatedtransistor; the other ends are connected to a common terminal 102. Oneend of transformer 96 is connected to the collector of transistor 91through a winding 103 on inductor 98 in turn connected in series with awinding 104 on inductor 97. Likewise, the other end of transformer 96 isconnected to the collector of transistor 92 through a winding 106 oninductor 97 in series with another winding 107 on inductor 98.

The B+terminal is connected to terminal 102 through a bias resistor 108.A bias capacitor 109 connects terminal 102 to the B- lead 93. Thisresistor and capacitor serve the same function as resistors 58, 59 andcapacitors 56, 57 in the FIG. 2 circuit.

The bases of transistors 91, 92 are connected by diodes 111, 112,respectively, to a common Zener diode 113 in turn connected to the B-lead 93. The common Zener diode 113 serves the same function asindividual Zener diodes 62, 64 in FIG. 2.

Shunt diodes 114, 116 are connected across the collector-emitterterminals of transistors 91, 92, respectively. A capacitor 117connecting the collectors of transistors 91, 92 restrains the rate ofvoltage rise on the collectors in a manner similar to thecollector-emitter capacitor 68 in FIG. 2.

Inductive-capacitive loading of the FIG. 7 inverter is accomplished by acapacitor 118 connected in series with with an inductor 119, thecombination being connected across the collectors of the transistors 91,92. A load 121 is connected across the capacitor 118.

FIG. 8 illustrates how an inverter loaded with a series capacitor 122and inductor 123 can be used to energize a "rapid-start"0 fluorescentlamp 124 (the details of the inverter circuit being omitted forsimplication). The lamp 124 has a pair of cathodes 126, 127 connectedacross the capacitor 122 for supply of operating voltage in a manneridentical to that previously described. In addition, the inductor 123comprises a pair of magnetically-coupled auxiliary windings 128, 129 forelectrically heating the cathodes 126, 127, respectively. A smallcapacitor 131 is connected in series with lamp 124.

In FIG. 10, the non-linear current-limiting means 132, 133 are shown asbeing two (small) incandescent lamps. However, other types of non-linearresistance means could be used as well.

Both the FIG. 9 circuit and the FIG. 10 circuit serve the same basicpurpose; which is that of preventing damage to the ballast circuit (suchas that if FIG. 2) in case the leads used for connecting to one of thelamp cathodes 126, 127 were to be accidentally shorted. This damageprevention is accomplished by providing for manifest limitation of themaximum amount of current that can be drawn from each one of theauxiliary windings 128, 129. In the circuit of FIG. 9, this manifestlimitation is accomplished by having the auxiliary windings 128, 129couple sufficiently loosely to the main inductor 123--such as byproviding a magnetic shunt between inductor 123 and the auxiliarywindings--thereby correspondingly limiting the degree of impactresulting from an accidental short circuit. Such a short circuit wouldresult in a net reduction in the effective inductance value of the tankinductor 123; which net reduction in inductance may in turn cause aprecipitous increase in the magnitude of the reactive current drawn fromthe inverter by the series-connected inductor 123 and capacitor 122,thereby causing damage to the inverter.

ADDITIONAL EXPLANATIONS AND COMMENTS

(a) With reference to FIGS. 2 and 5, adjustment of the amount of powersupplied to load 26', and thereby the amount of light provided by lamp71, may be accomplished by applying a voltage of adjustable magnitude toinput terminals IPl and IP2 of the Toroid Heater; which is thermallycoupled with the toroidal ferrite cores of saturable transformers 47,49.

To avoid such self-destruction, arrangements can readily be made wherebythe very act of removing the load automatically establishes a situationthat prevents the possible destruction of the power supply andballasting means. For instance, with the tank capacitor (52) beingpermanently connected with the lamp load (11)--thereby automaticallybeing removed whenever the lamp is removed--the inverter circuit isprotected from self-destruction.

(d) At frequencies above a few kHz, the load represented by afluorescent lamp--once it is ignited--is substantially resistive. Thus,with the voltage across lamp 11 being of a substantially sinusoidalwaveform (as indicated in FIG. 3d), the current through the lamp willalso be substantially sinusoidal in waveshape.

(e) In the fluorescent lamp unit of FIG. 1, fluorescent lamp 11 isconnected with power supply and ballasting circuit 16 in the exact samemanner as is load 26 connected with the circuit of FIG. 2. That is, itis connected in parallel with the tank capacitor (52) of the L-Cseries-resonant circuit. As is conventional in instant-start fluorescentlamps--such as lamp 11 of FIG. 1--the two terminals from each cathodeare shorted together, thereby to constitute a situation where eachcathode effectively is represented by only a single terminal. However,it is not necessary that the two terminals from each cathode be shortedtogether; in which case--for instant-start operation--connection from alamp's power supply and ballasting means need only be made with one ofthe terminals of each cathode.

(f) It is thought that the present invention and many of its attendantadvantages will be understood from the foregoing description and thatmany changes may be made in the form and construction of its componentsparts, the form described being merely a preferred embodiment of theinvention.

I claim:
 1. An arrangement comprising:power input terminals across whichis provided an ordinary AC power line voltage; rectifier means connectedwith the power input termnials; the rectifier means having; (i) a centerterminal, (ii) a positive terminal, and (iii) a negative terminal; thecenter terminal being connected, substantially wihtout any interveningimpedance, with one of the power input terminals; the rectifier meansbeing operative to provide a DC voltage between the negative terminaland the positive termina; the magnitude of this DC voltage beingsubstantially constant and approximately equal to that of thepeak-to-peak magnitude of the AC power line voltage; inverter meansconneced with: (i) the center terminal, (ii) the negative terminal, and(iii) the positive terminal; the inverter means being operative toprovide a squarewave voltage at an inverter output; the squarewavevoltage having an absolute peak-to-peak magnitude substantially equal tothat of the AC power line voltage; an L-C voltage connected with theinverter output; the L-C circuit having a tank inductor and a tankcapacitor; the L-C circuit being naturally resonant at or near thefundamental frequency of the squarewave voltage; and fluorescent lampeffectively connected in parallel with the tank capacitor, thereby toreceive a lamp current.
 2. The arrangement of claim 1 includingadjustment means functional to permit control of the fundamentalfrequency of the squarewave voltage, thereby to permit control of themagnitude of the lamp current.
 3. The arrangement of claim 1 includingcontrol means functional, in response to the provision of a controlaction, to control the magnitude of the lamp current.
 4. The arrangementof claim 1 including control means functional, in response to receivinga control signal at a control input, to control the magnitude of thelamp current.
 5. The arrangement of claim 4 wherien the cotnrol input iselectrically isolated from the power input terminals, thereby to preventthe flow of current between the power input terminals and the controlinput.
 6. The arrangement of claim 1 wherein the lamp current has asubstantially sinusoidal waveshape.
 7. The arrangement of claim 1wherein: (i) the fluorescent lamp has a pair of lamp terminals, and (ii)an electrical conduction path exists between the lamp terminals and thepower input terminals.
 8. An arrangement comprising:power inputterminals across which is provided an ordinary AC power line voltage;rectifier means connected with the power input terminals and operativeto provide a DC voltage at a set of DC terminals; and inverter ballastmeans connected with the DC terminals and operative to provide analternating output current to a gas discharge lamp connected across apair of output terminals; the inverter ballast means including: (i)frequency-dependent impedance means, and (ii) control means operative,in response to manifest control action, to control the fundamentalfrequency of the alternating current, thereby to effect adjustment ofthe magnitude of the output current; the control means has a controlinput receptive of said manifest control action; the control input beingelectrically isolated from the power input terminals, thereby to preventthe flow of current between the power input terminals and the controlinput.
 9. The arrangement of claim 8 wherein the inverter ballast meansis characterized by including an inverter means operative to provide asquarewave output voltage having peak-to-peak magnitude substantiallyequal to that of the AC power line voltage.
 10. The arrngement of claim8 wherein: (i) the set of DC terminals includes a negative terminal, apositive terminal, and a center tap; and (ii) the center-tap isconnected with one of the power input terminals substantially withoutany intervening impedance.
 11. The arrangement of claim 10 wherein: (i)the DC voltage is provided between the negative terminal and thepositive terminal; and (ii) the magnitude of the DC voltage issubstantially constant and approximately equal to the absolutepeak-to-peak magnitude of the AC power line voltage.
 12. An arrangementcomprising:power input terminals across which is provide dan ordinary ACpower line voltage; rectifier means connected with the power inputterminals and operative to provide a DC voltage at a set of DCterminals; gas discharge lamp having a pair of lamp terminals; andinverter ballast means connected with the DC terminals and operative toprovide an alternating output current at a pair of output terminals; theoutput terminals being connected with the lamp terminals; the inverterballast means including: (i) frequency-dependent impedance means, and(ii) control means operative, in response to manifest control actionprovided at a set of control input terminals, to control the fundamentalfrequency of the alternating current, thereby to effect adjustment ofthe magnitude of the output current; the control input terminals beingelectrically isolated from the power input terminals, thereby to preventthe flow of current between the power input terminals and the cotnrolinput terminals.
 13. The arrangement of claim 12 wherien said controlaction is provided in the form of a control voltage provided at the setof control input terminals.
 14. The arrangement of cliam 13 includingmeans for adjusting the magnitude of the control voltage, thereby toadjust the magnitude of the output current.
 15. The arrangement of claim12 wherein the inverter means provides at an inverter output asquarewave voltage having peak magnitude approximately equal to that ofthe AC power line voltage.
 16. An arrangement comprising:power inputterminals across which is provided an ordinary AC power line voltage;rectifier means connected with the power input terminals and operativeto provide a DC voltage at a set of DC terminals; gas discharge lamphaving a pair of lamp terminals as well as a pair of thermioniccathodes; each lamp terminal being connected with one of the thermioniccathodes; each thermionic cathode having a pair of cathode terminals;inverter means connected with the DC terminals and operative to providean alternating inverter output voltage at a set of inverter outputterminals; and tuned circuit means connected between the inverter outputterminals and the lamp terminals, thereby to provide lamp operatingvoltage to the lamp terminals; the tuned circuit means including acapacitor and an inductor operative to resonantly interact at thefundamental frequency of the alternating inverter output voltage,thereby to provide for the lamp operating voltage to have a magnitudethat is substantially higher before lamp ignition than after lampignition; a pair of auxiliary windings being magnetically coupled withthe inductor; each auxiliary winding being connected with one of thethermionic cathodes, thereby to provide a cathode heating voltagethereto.
 17. An arrangement comprising:power input terminals acrosswhich is provided an ordinary AC power line voltage; rectifier meansconnected with the power input terminals and operative to provide a DCvoltage at a set of DC terminals; gas discharge lamp having a pair oflamp terminals as well as a pair of thermionic catodes; each lampterminal being connected with one of the thermionic cathodes; eachthermionic cathode having a pair of cathode terminals; inverter meansconnected with the DC terminals and operative to provide an alternatinginverter output voltage at a set of inverter output terminals; andcircuit means connected between the inverter output terminals and thelamp terminals, thereby to provide lamp operating voltage to the lampterminals; the circuit means having a pair of auxiliary output terminalsat which is provided a cathode heating voltage; the pair of auxiliaryoutput terminals being connected with one of the pairs of cathodeterminals, thereby to provide a cathode heating voltage thereacross; thecathode heating voltage having a magnitude that is substantially higherbefore lamp ignition than it is after lamp ignition.
 18. The arrangementof claim 17 wherein the magnitude of the cathode heating voltage is atleast about 50% higher before lamp ignition than it is after lampignition.
 19. An arrangement comprising:power input terminals acrosswhich is provided an ordinary AC power line voltage; rectifier meansconnected with the power input terminals and operative to provide a DCvoltage at a set of DC terminals; and inverter ballast means connectedwith the DC terminals and operative to provide an alternating outputcurrent to a gas discharge lamp connected across a pair of outputterminals; the inverter ballast means including control means operative,in response to a control signal provided at a pair of control inputterminals; to control the magnitude of the alternating output currentprovided to the gas discharge lamp; the control input terminals beingelectrically isolated from the power input terminals, thereby to preventthe flow of current between the power input terminals and the controlinput.
 20. An arrangement comprising:power input terminals across whichis provided an ordinary AC power line voltage; rectifier means connectedwith the power input terminals and operative to provide a DC voltage ata set of DC terminals; gas discharge lamp having a pair of lamp terminalas well as a pair of thermionic cathodes; each lamp terminal beingconnected with one of the tehrmionic cathodes; each thermionic cathodehaving a pair of cathode terminals; and inverter ballast means connectedwith the DC terminals and operative to provide an alternating outputvoltage at a pair of ballast output terminals as well as an auxiliaryvoltage at a pair of auxiliary terminals; the lamp terminals beingconnected with the ballast output terminals; one of the pair sof cathodeterminals being connected with the auxiliary terminals; the auxiliaryvoltage having a magnitude that is substantially higher during periodswhen the gas discharge lamp fails to draw current from the ballastoutput terminals, such as prior to lamp ignition, as compared withperiods during which the gas discharge lamp does draw current from theballast output terminals, such as after lamp ignition.